The invention relates to an insulation element, as can be used for instance for heat and/or sound insulation, at least one nonwoven layer and/or a foam layer being enclosed by a film layer.
Insulation elements of this type are already known in various forms. Reference is made for example to DE 198 48 679 A1. Since insulation elements of this type are also used with preference in aircraft construction, a flame-retardant property is considered important. As disclosed by the above document, it has already been proposed to produce the film layer from aluminium-metallized polyethylene or, possibly, also from inherently flame-resistant polymers. In addition, if a foam layer is being used, it has been proposed to use a polyimide foam layer.
On the other hand, in the case of insulation elements of this type there is also the requirement that the enclosure should be permeable to water vapour.
However, so far it has not been possible to combine the property of water vapour permeability, possibly even directionally-dependent water vapour permeability, with the desired flame-retardant property of the insulating element, including with regard to its enclosure.
On this basis, the invention is concerned with the technical object of providing an insulation element which, on the one hand, is permeable to vapour diffusion, in the desired way, but on the other hand also meets as far as possible the high requirements for flame-retardant properties of the insulation element.
This object is achieved initially and substantially in the case of the subject matter of claim 1, it being provided that the film layer consists of a flame-retardant material, that the film layer also has through-openings and that the through-openings are open to vapour diffusion. The invention consequently takes the approach of forming the film layer or, as also emerges from the text below, preferably an outer film layer, only with a predominantly flame-retardant effect, but to leave through-openings which, although closed by the film, are open to vapour diffusion. The film layer itself can consequently be not permeable to vapour diffusion, or possibly only much less permeable to vapour diffusion. A first, more specific embodiment of this teaching proposes that the through-openings comprise cut-outs formed in the film layer and that these cut-outs are respectively closed by a second film of material which is open to vapour diffusion, disposed in a window-like manner. Consequently, punched openings, hole-like punched openings, can be made in the film layer and then be covered with individual, patch-like portions of a second film. For example, the second film may be adhesively bonded to the outer film layer to the extent that the cut-outs are closed by it. A very wide range of geometries can be used for the cut-outs, and this also applies to the embodiments still to be described below. For example, circular, rectangular, star-shaped, grid-like, and so on. In a further specific embodiment, the invention also proposes that the second film is disposed under the outer film layer and in such a way that it covers the latter even in the regions without through-openings. Consequently, film layers simply lying one on top of the other may be provided, the outer film layer being formed by the flame-retardant material and the inner film layer being formed by the material open to vapour diffusion, with the outer film layer having through-openings and the film layer which is open to vapour diffusion having no openings.
Furthermore, it is possible in principle for these film layers to surround the nonwoven and/or foam layer (or possibly a number of these layers) separately in each case and independently of one another. In addition, these film layers may all be welded at the edges (resulting in the example last described in four layers on top of one other at a seam). In addition, however, it may also be provided that the outer film layer is laminated to the second film. Adhesive bonding can be brought about just by using the adhesiveness of the film layer and/or of the second film. The films may also be bonded to one another by a separate adhesive or a separate layer of adhesive. In the latter case, it is recommendable, however, to provide the layer of adhesive also only in a grid-like manner, in order to preserve the vapour-diffusing property of the second film over as large a surface area as possible, in any event in the regions of the through-openings.
In a further embodiment, it is also proposed that a third film layer is disposed under the second film layer and that the third film layer also consists of a flame-retardant material, but has through-openings which are open to vapour diffusion.
With regard to the flame-retardant material, polyimide is particularly suitable and is already available on the market as polyimide films. However, a polyphenylene sulphide (PPS) film may also be used, for example. Also, a polyester (PET) film, a polyvinyl-fluoride (PVD) or polyvinyl-difluoride (PVDF) film.